Causation and Acute Viral Diseases

Abstract

The discovery of viruses, their growth in mice, in tissue culture, and in embryonated eggs brought new problems in causation and reemphasized the limitations of the original Henle—Koch postulates. Dr. Thomas Rivers (Figure 3.1), the distinguished American virologist, discussed these issues in his presidential address before the American Society of Immunology in 1937 (Rivers, 1937). Dr. Rivers had headed the virology research program at the Rockefeller Foundation and, with Frank Horsfall, had edited one of the first great texts in virology (Rivers and Horsfall, 1959). In his lecture, he pointed out that blind adherence to Koch’s postulates might sometimes act as a hindrance rather than an aid. For example, the idea that an infectious malady can be caused only by the action of a single agent is incorrect. If Shope had adhered to this notion, he would never have discovered that swine influenza as it occurs in nature is caused by the combined or synergistic action of two agents, one a virus not cultivable on lifeless media, the other an ordinary hemophilic bacterium (Shope, 1931). The requirement that the infectious agent be grown in a pure state on lifeless media also hindered the establishment of the causal relation of viruses to disease, because viruses require living tissues for propagation, as in chick embryo or tissue culture. Thus, Rivers felt that “Koch’s postulates have not been fulfilled in viral diseases.” In their place he suggested the conditions to be met before the specific relation of a virus to a disease is established (Table 3.1).